clap/examples/07_option_args.md
Ed Page bfa02fd418 test: More thoroughly test examples
This ports our example testing over to [trycmd](https://docs.rs/) so
we can:
- More thoroughly test our examples
- Provide always-up-to-date example usage

The old way of testing automatically picked up examples.  This new way
requires we have a `.md` file that uses the example in some way.

Notes:
- Moved overall example description to the `.md` file
- I added cross-linking between related examples
- `14_groups` had a redundant paragraph (twice talked about "one and
  only one"
2021-11-23 13:13:41 -06:00

77 lines
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Markdown

Option arguments are those that take an additional value, such as "-c value". In clap they
support three types of specification, those with short() as "-o some", or those with long()
as "--option value" or "--option=value"
Options also support a multiple setting, which is discussed in the example below.
Let's look at their help:
```bash
$ 07_option_args --help
MyApp
USAGE:
07_option_args[EXE] [OPTIONS] --input <input> [output]
ARGS:
<output> the output file to use
OPTIONS:
-c, --config <FILE> the config file to use
-h, --help Print help information
-i, --input <input> the input file to use
```
First, we see that `--input` is required:
```bash
$ 07_option_args
? failed
error: The following required arguments were not provided:
--config <FILE>
--input <input>
USAGE:
07_option_args[EXE] [OPTIONS] --input <input> [output]
For more information try --help
```
But `--input` also requires `--config`:
```bash
$ 07_option_args --input input.txt --input another.txt
? failed
error: The following required arguments were not provided:
--config <FILE>
USAGE:
07_option_args[EXE] [OPTIONS] --input <input> --config <FILE> [output]
For more information try --help
```
Everything works now that we specify both:
```bash
$ 07_option_args --input input.txt --input another.txt --config config.toml
An input file was specified
An input file: input.txt
An input file: input.txt
An input file: another.txt
The "input" argument was used 2 times
```
But we can't mix this with output:
```bash
$ 07_option_args --input input.txt --input another.txt --config config.toml output.txt
? failed
error: The argument '<output>' cannot be used with '--input <input>'
USAGE:
07_option_args[EXE] --input <input> --input <input> --config <FILE>
For more information try --help
```
That requires passing it in by itself:
```bash
$ 07_option_args output.txt
The "input" argument was used 0 times
```